/Engine/Plugins/Runtime/XRBase/Source/XRBase/Public/MotionTrackedDeviceFunctionLibrary.h
Get the maximum number of controllers that can be tracked.
(int) number of controllers that can be tracked, or -1 if there is no limit (IsMotionTrackedDeviceCountManagementNecessary()should return false).
[UFUNCTION](Programming/UnrealArchitecture/Reference/Functions)(BlueprintPure, Category="Input|MotionTracking") static int32 GetMaximumMotionTrackedControllerCount()